Ahhhh, a most interesting question, and one I (may) have to deal with in my PhD. Walvisteuthis virilis was placed in its own family, Walvisteuthidae, by Nesis & Nikitina when they described it in 1986, because it had some very unusual characteristics, including the tentacle club morphology. Subsequently Young et al. (on the Tree of Life link you gave) deemed this species a junior synonym of Onykia rancureli Okutani, 1981. Since Young et al. consider 'virilis' and 'rancureli' to refer to the same species, the older name (rancureli) is the valid one, IF these species are the same (more on that in a minute). However, this/these species is/are different enough from the other onychoteuthids to deserve its/their own genus, so the new genus name, Walvisteuthis, was kept, giving the new binomial 'Walvisteuthis rancureli.'
Problem is, the two type specimens described (see O. rancurelihere and W. virilishere on the Tree of Life) do have some similarities, but also some very striking differences, such as the presence of teeth on the sucker rings in W. virilis (all other onychoteuthid species have completely smooth, toothless sucker rings), and the very, very strange morphology of the tentacle clubs in the W. virilis holotype.
So far I have not been able to examine a specimen of W. virilis - the holotype is at the Zoological Museum, Moscow State University, where I hope to be making a collection visit later this year, and the nice specimen in the ToL photo was not available when I went to the Smithsonian. I have examined one of the paratypes of O. rancureli and it certainly had smooth sucker rings and tentacle clubs that did not look like those described/figured for W. virilis, so I have some pretty strong reservations about the synonymy, but since I haven't examined any W. virilis myself, I'm not *actually* qualified to make any judgement yet.
In short... the family Walvisteuthidae may or may not exist; and the genus Walvisteuthis belongs either in the Onychoteuthidae or its own family, and currently contains a single species, which could either be virilis as originally described or the older name rancureli if these two species prove to be one and the same; BUT there is also a possbility that O. rancureli and W. virilis could be two species in the same genus, in which case Walvisteuthis would have two species.
Aren't you glad you asked? If/when I get to examine a W. virilis specimen, I'll post a follow-up here.

Onykia rancureli was described in 1981, Walvisteuthis virilis was decribed in 1986. Lately Tsuchiya has reviewed these species and decided that W. virilis is a synonym of O. rancureli (the earlier name has priority) but different from the other Onykia species so the generic name Walvisteuthis is used. So the official (for the time being) name isWalvisteuthis rancureli (Okutani) 1981, the authors name in parentheses meaning the generic assignment has changed from the original description.

From the TOL page:

Nomenclature

Nesis and Nikitina (1986) described a new family of squids, "Walvisteuthidae", based on a mature male which they named Walvisteuthis virilis. The squid was somewhat similar to onychoteuthids but it had a number of very peculiar features that caused the authors to erect the new family. The status of this family has recently been reviewed by Tsuchiya (in preparation) and he concluded that Walvisteuthis virilis is a synonym of the onychoteuthid, Onykia rancureli. The peculiar features appear to be modifications that arise at sexual maturity. "Onykia" rancureli has been widely recognized as being very different from other members of this genus and several authors have suggested that a new generic name is needed (e.g., Toll, 1982; Tsuchiya and Okutani, 1991). This generic name is Walvisteuthis.